1. Field of the Invention
This invention concerns a process for converting solid hydrocarbon materials present in a subterranean formation into a gaseous material which can be recovered from the formation and utilized for fuel or other purposes.
2. Description of the Prior Art
Many subterranean, hydrocarbon containing deposits are not amenable to the recovery of the hydrocarbon materials by primary recovery because the hydrocarbon materials are too viscous to flow even if a pressure differential is applied to the material and the materials are present in a permeable formation. For example, tar sand deposits as are found in the western part of the United States and in the northern part of Alberta, Canada contain vast quantities of bituminous petroleum, but essentially no material may be recovered by so called primary means because the viscosity of the bituminous petroleum at reservoir conditions is in the range of millions of centipoise. Accordingly, some form of supplemental recovery process must be applied to these tar sand materials, as well as to other subterranean, viscous petroleum containing formations, in order to recover any appreciable amount of hydrocarbon fluids therefrom.
In the case of the tar sand deposits, a particularly promising supplemental recovery technique has been disclosed in copending application, Ser. No. 481,581 filed June 21, 1974 and in Ser. No. 481,582 filed June 21, 1974, which generally involves the use of a critical ratio of air and steam to achieve a controlled low temperature oxidation reaction which propagates rapidly throughout the tar sand material, mobilizing an appreciable quantity of viscous petroleum present in the formation, and results in recovering up to about 75 percent of the petroleum in place. This recovery technique is different from the conventional in situ combustion process and more successful when applied to formations similar to the tar sand deposits, because the permeabiliy of the tar sand deposit is too low to permit application thereto of conventional in situ combustion as is practiced in more conventional oil reservoirs. Although this process results in an unusually high percentage recovery as compared to other supplemental recovery processes for use in tar sand deposits, a carbon residue does remain on the sand grains in the formation after termination of a controlled oxidation reaction.
It is known by persons skilled in the art, and amply described in the literature, that many viscous liquid hydrocarbon materials, and under certain conditions granulated solid hydrocarbon materials, may be converted to a synthesis gas by subjecting the hydrocarbon materials to steam and oxygen under controlled conditions in a suitably fabricated reactor. For example, the following U.S. Patents deal with various aspects of gasification of liquid or solid carbonaceous materials in surface reactors under conditions of high temperature and pressure. U.S. Pat. No. 2,864,677, Eastman, et al.; U.S. Pat. No. 2,976,134, Paull; U.S. Pat. No. 2,992,907, Atwell; U.S. Pat. No. 3,097,081, Eastman, et al.; U.S. Pat. No. 3,556,751, Slater, et al.; and U.S. Pat. No. 3,709,669, Marion, et al. All of these patents deal with methods whereby synthesis gas, specifically carbon monoxide and hydrogen, may be produced from solid or viscous liquid hydrocarbon materials in a high pressure, high temperature reactor by reaction with steam and oxygen.
In those instances where some portion of the lower molecular weight hydrocarbons have been recovered from subsurface deposits such as from tar sand deposits, the percentage of hydrocarbon materials remaining is too small to justify mining operations, although the total amount of hydrocarbon present in these formations is considerable because of their vast volumes there is a substantial need for a method which will permit recovery and utilization of hydrocarbon materials present in subsurface formations. There is particularly a need for a method which will permit recovery of essentially solid and otherwise unrecoverable hydrocarbon materials by converting the solid materials into a gaseous form within the reservoir itself, and recovering the gaseous form materials from the formation where they may be utilized as fuel or feed gas for manufacturing operations.